Just for reference, a stock 2500k is over 50% faster than a stock q9550, and while that doesn't come into play in certain games, it does have an effect in most modern games. Unless you also intend to upgrade your CPU in the next 6-12 months, don't spend over about $220 on your GPU.

Thanks everyone for valuable advice, specially Termie. I am planning an update in 12-18 month period, but will I be able to play current games like Black Ops-2 and Crysis-3 at reasonable frame rate with current hardware by adding 7870 or 7950?

Thanks everyone for valuable advice, specially Termie. I am planning an update in 12-18 month period, but will I be able to play current games like Black Ops-2 and Crysis-3 at reasonable frame rate with current hardware by adding 7870 or 7950?

12-18 months is a long time. You're talking about the successor to Haswell, potentially.

Think of it this way: for $210 today, you can buy an HD7870 that will not be maxed out in any modern game on your CPU, and use the money saved towards buying a GPU that will be 50% faster for $150 in 18 months.

Or, you could spend $280 today for an HD7950, get essentially the exact same performance as you would on an HD7870 for 18 months, and then not have saved any money towards buying a new GPU that will be faster for $150.

Truth of the matter is, you would definitely see the benefits of a GPU upgrade now, but your CPU is right behind it in terms of needing an upgrade. If you have $300 total, spend $210 today on a GPU and put the rest towards a CPU upgrade in the spring. Multiple forum members here have recently upgraded older quad systems (not to mention dual systems) for gaming and found new CPUs to have a significant effect. The HD7870 is no slouch - you're talking 3x faster than your current GPU, versus perhaps 3.5x faster with an HD7950.